Heat-Stable Concentrated Milk Product

ABSTRACT

The invention provides a stable concentrated dairy liquid, such as concentrated milk, with improved flavor, color, and mouthfeel, and a method of production thereof. The method utilizes specific thermal treatments to produce the stable concentrated dairy liquid to which a stabilizer and mouthfeel enhancer are added. The resulting products have a sterilization value F o  of at least 5 that is also resistant to gelling and browning during high temperature sterilization and is also resistant to gelling and browning during storage for greater than six months. The method balances such thermal treatments with addition of stabilizer and enhancer to achieve the desired flavor/mouthfeel and sterilization and to achieve reduced level of soluble protein in the concentrated milk prior to concentration to resist gelation and minimize browning. Moreover, such processing may be utilized in a milk that is concentrated to a factor of 2.7 fold or higher and contains at least 8.5 percent protein.

RELATED APPLICATIONS

This application is a divisional of prior application Ser. No.11/186,543, filed Jul. 21, 2005, which claims benefit of U.S.Provisional Application 60/590,696, filed Jul. 23, 2004, and U.S.Provisional Application 60/679,267, filed May 9, 2005, all of which arehereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

This invention relates to concentrated dairy products. Morespecifically, this invention relates to non-gelling, non-browning,organoleptically pleasing, concentrated dairy products, such asconcentrated milk, and methods for producing the same.

BACKGROUND OF THE INVENTION

Liquid dairy products, such as milk, may be thermally processed toincrease their stability. Unfortunately, thermally treating milk oftenresults in color changes and/or gelation during processing or extendedstorage. For example, lactose in milk heated to high temperatures tendsto interact with proteins and results in an unsightly brown color. Thisundesired condition is often referred to as “browning” or a “browningreaction.” Gelation, on the other hand, is not completely understood,but the literature suggests that gels may form, under certainconditions, as a three-dimensional protein matrix formed by the wheyproteins. See, e.g., Datta et al., “Age Gelation of UHT Milk—A Review,”Trans. IChemE, Vol. 79, Part C, 197-210 (2001). Both gelation andbrowning are undesirable in milk since they impart objectionableorganoleptic properties. Although a limited amount of browning can beaccepted, it is preferred that no gelation or protein aggregation isvisible.

The concentration of milk is often desired because it allows for smallerquantities to be stored and transported, thereby resulting in decreasedstorage and shipping costs, and may allow for the packaging and use ofmilk in more efficient ways. However, the production of anorganoleptically-pleasing, highly concentrated milk can be difficult,because the concentration of milk generates even more pronouncedproblems with gelation and browning. For instance, milk that has beenconcentrated at least three fold (3×) has an even greater tendency toundergo protein gelation and browning during its thermal processing.Additionally, such concentrated milk also has a greater tendency toseparate and form gels over time as the product ages, thereby limitingthe usable shelf life of the product. Concentrated milk, as a result, isgenerally limited to concentrations below about 25 percent total solids,protein levels below about 7 percent, and a shelf life of less than 6months.

Numerous studies have been reported on gelation and browning of milk andconcentrated milk and many factors affecting gelation in milk have beenidentified. Examples of such factors include calcium (chelation and/orremoval), mode and severity of thermal treatment, proteolysis, milkproduction factors, microbiological quality of raw milk, storagetemperature and time, additives, fat content, pH, and the polymerizationof casein. See, e.g., Udabage et al., “Effects of Mineral Salts andCalcium Chelating Agents on the Gelation of Renneted Skim Milk,”84:1569-1575 (2001); Cano-Ruiz et al., “Changes in PhysicochemicalProperties of Retort-Sterilized Dairy Beverages During Storage,” J.Dairy Sci. 81:2116-2123 (1998); El-Din et al., “Polymerization of Caseinon Heating Milk,” Int. Dairy J. 3:581-588 (1993); McMahon et al.,“Effects of Phosphate and Citrate on the Gelation Properties of CaseinMicelles in Renneted Ultra-high Temperature (UHT) SterilizedConcentrated Milk,” Food Structure, Vol. 10, 27-36 (1991); Harwalkar etal., “Effect of Added Phosphates and Storage on Changes in Ultra-HighTemperature Show Time Sterilized Concentrated Skim Milk. 1. Viscosity,Gelation, Alcohol Stability, Chemical and Electrophoretic Analysis ofProteins,” Neth. Milk Dairy J. 32:94-111 (1978).

The production of concentrated milk, also known as evaporated milk, isknown in the art and may be produced from whole milk, partly skimmedmilk, or skim milk. Unfortunately, as noted above, the concentration andshelf life of typical concentrated milk may be limited due to gelationand browning problems. Typically, as noted above, concentrated milkproducts are limited to less than 25 percent total solids, less than 7percent protein, and have shelf lives of less than 12 months, and oftensignificantly less, due to age gelation.

A typical method of producing concentrated milk involves multipleheating steps in combination with the concentration of the milk. Forexample, one general method used to produce concentrated milk involvesfirst standardizing the milk to a desired ratio of solids to fat andthen forewarming the milk to reduce the risk of the milk casein fromcoagulating during later sterilization. Forewarming also decreases therisk of coagulation taking place during storage prior to sterilizationand may further decrease the initial microbial load. The forewarmed milkis then concentrated by evaporation, ultrafiltration, or otherappropriate methods to the desired concentration. The milk may behomogenized, cooled, restandardized, and packaged. In addition, astabilizer salt may be added to help reduce the risk of coagulation ofthe milk that may occur at high temperatures or during storage. Eitherbefore or after packaging, the product is sterilized. Sterilizationusually involves either relatively low temperatures for relatively longperiods of time (e.g., about 90 to about 120° C. for about 5 to about 30minutes) or relatively high temperatures for relatively short periods oftime (e.g., about 135° C. or higher for a few seconds).

The degree of sterilization or the sterilization value (F_(o)) is basedon the time that the dairy product is subjected to specific temperaturesand is a culmination of all thermal treatments that the productencounters during processing. Consequently, a desired sterilizationvalue may be achieved through a variety of processing conditions.Typically, concentrated milk is sterilized to a F_(o) of at least 5 andpreferably to a much higher level (e.g., 15 or higher). Unfortunately,as discussed above, high temperatures or long exposures to elevatedtemperatures, as are generally necessary in conventional sterilizationmethods to achieve the desired sterilization values, also adverselyaffect the long term stability of concentrated milk, especiallyconcentrated milk with greater than about 7 percent protein, by inducinggelation or browning.

The sterilization value for a sterilization process can be measuredusing graphical integration of time-temperature data during the food'sslowest heating point rate curve for the thermal process. This graphicalintegration obtains the total lethality provided to the product. Tocalculate the processing time required to achieve a desired F_(o) usingthe graphical method, a heat penetration curve (i.e., a graphical plotof temperature versus time) at the slowest heating location of the foodis required. The heating plots are then subdivided into small timeincrements and the arithmetic mean temperature for each time incrementis calculated and used to determine lethality (L) for each meantemperature using the formula:

L=10^((T-121)/z)

Where:

-   -   T=arithmetic mean temperature for a small time increment in °        C.;    -   z=standardized value for the particular microorganism; and    -   L=lethality of a particular micro-organism at temperature T.

Next, the lethality value calculated above for each small time incrementis multiplied by the time increment and then summed to obtain thesterilization value (F_(o)) using the formula:

F _(o)=(t _(T1))(L ₁)+(t _(T2))(L ₂)+(t _(T3))(L ₃)+ . . .

Where:

-   -   t_(T1), t_(T2), . . . =Time increment at temperature T1, T2, . .        . ;    -   L₁, L₂, . . . =Lethality value for time increment 1, time        increment 2, . . . ; and    -   F_(o)=Sterilization value at 121° C. of a microorganism.

Consequently, once a penetration curve is generated, the sterilizationvalue F_(o) for the process can be computed by converting the length ofprocess time at any temperature to an equivalent process time at areference temperature of 121° C. (250° F.). Jay, 1998, “High TemperatureFood Preservation and Characteristics of Thermophilic Microorganisms,”in Modern Food Microbiology (D. R. Heldman, ed.), ch. 16, New York,Aspen Publishers.

Various approaches for the production of concentrated milk have beendocumented. For example, Wilcox, U.S. Pat. No. 2,860,057, discloses amethod to produce a concentrated milk using forewarming, pasteurizing,and high-temperature, short-term sterilization after concentration.Wilcox teaches the concentration of milk to approximately 26 percentsolids using forewarming at about 115° C. (240° F.) for about 2 minutesprior to concentration, preheating at 93° C. (200° F.) for about 5minutes after concentration, and sterilization at about 127 to 132° C.(261 to 270° F.) for 1 to 3 minutes.

Blake, U.S. Pat. No. 4,282,262, is directed to a method to produce dairybased mixes for frozen desserts. Blake discloses a milk-blend fractioncomprising a specially prepared concentrated blend of milk, sugar,stabilizer salts, and casein-reactive gums. Blake teaches theconcentration of a milk having between about 1 to 9 percent fat andadded stabilizer salts to about 25 to 36 percent total solids, afterwhich the various other components are blended therein. Initially,forewarming is continued until the milk has a standard whey proteinnitrogen test ranging from 4.5 to 5.5. The concentrated milk blend isthen sterilized by heating at 104 to 148° C. (220 to 300° F.) for 1 to 8seconds.

Reaves et al., U.S. Patent Publication 20030054079 (Mar. 20, 2003),discloses a method of producing an ultra-high temperature milkconcentrate having 30 to 45 percent nonfat milk solids. Reaves et al.teach the preheating of milk for 10 minutes at 65° C. (150° F.) toproduce a preheated, milk starting product, which is then pasteurized at82° C. (180° F.) for 16 to 22 seconds and evaporated under elevatedpasteurizing temperatures (i.e., 10 minutes at 62° C. (145° F.) undervacuum) to produce an intermediate, condensed liquid milk. A cream andstabilizer, such as sodium hexametaphosphate or carrageenan, are addedto the intermediate milk, which is then ultrapasteurized in two stageswherein the first stage is at 82° C. (180° F.) for 30 to 36 seconds andsecond stage is at 143° C. (290° F.) for 4 seconds. Shelf lives of 30days to 6 months are reported for the resulting milk concentrate.

As indicated, concentrated milks require thermal processing tosterilize. The use of such elevated temperatures and increased exposureto such temperatures are factors that may contribute to undesirableproperties in the milk, such as gelation and browning. Unfortunately,higher concentrations, such as protein levels greater than about 7percent that are desired for efficiency and logistical standpoints,often make these undesirable conditions even more pronounced anddifficult to avoid. Consequently, there is a desire for improvedconcentrated milks (generally 3× or higher and containing more than 7percent protein) that are non-gelling and non-browning for greater thanabout 6 months storage at ambient conditions. There is also a desire forimproved methods to produce such concentrated milks using a thermaltreatment sufficient to sterilize and at the same time prevent gelformation and minimize browning. The present invention provides suchcompositions and methods.

SUMMARY OF THE INVENTION

The invention is directed to a stable concentrated dairy liquid, such asconcentrated milk, and a method of production thereof. The stableconcentrated dairy liquid comprises a dairy liquid containing at leastabout 8.5 percent protein, wherein the protein comprises serum proteinand casein protein, wherein the dairy liquid is forewarmed prior toconcentration, wherein ultrafiltration, with or without diafiltration,is used to concentrate the dairy liquid, wherein certain components(i.e., stabilizers and mouthfeel enhancers) are added back to theconcentrated dairy liquid after concentration, and wherein the resultingproduct is subjected to a heat treatment (e.g., retorting) to achieve aF_(o) value of at least 5. Generally, the resulting concentrated dairyliquid is concentrated about 2.7 fold or higher, preferably about 3 foldor higher, and more preferably about 4 fold or higher; if desired, theresulting concentrated dairy liquid may be standardized prior to achievea more uniform and consistent concentration level over the same and/ordifferent production runs. Furthermore, the resulting concentrated dairyliquid has a sterilization value F_(o) of at least 5 (preferably atleast about 6.5 and more preferably at least about 7.5), and isresistant to gel formation and browning during both high temperatureprocessing conditions and ambient storage conditions for at least 6months (preferably at least about 9 months and more preferably at leastabout 12 months). In preferred embodiments, the F_(o) value is about 5to about 10. Especially preferred concentrated dairy liquids include 3×to 5× concentrates having at least about 8.5 percent protein, in anotheraspect at least about 8.8 percent protein, and in another aspect atleast about 9 percent protein.

The method to produce such stable concentrated dairy liquid utilizesspecific thermal treatments to produce a stable dairy liquid, which isconcentrated to at least 2.7 fold and preferably to at least 3 fold. Themethod also produces a dairy liquid having a sterilization or F_(o)value of at least 5 (preferably at least about 6.5 and more preferablyat least about 7.5) that is also resistant to gelling and browningduring high temperature treatment of sterilization and during storageunder ambient conditions for greater than 6 months (preferably at leastabout 9 months and more preferably at least about 12 months). The methodbalances such thermal treatments to achieve the desired sterilizationand, at the same time, to achieve sufficient crosslinking of serumprotein in the concentrated milk to resist gelation and minimizebrowning reactions; the addition of certain components (i.e.,stabilizers and mouthfeel enhancers) after ultrafiltration step improvesstability and significantly enhances mouthfeel and other organolepticproperties. Indeed, mouthfeel and other organoleptic properties are veryclose to the starting dairy liquid.

The dairy liquid is forewarmed prior to concentration in order toprovide a more stable concentrated final product. Generally, theforewarming comprises treating the starting dairy liquid to atemperature and for a time effective to provide a reduced amount ofsoluble protein. For purposes of this invention, “a reduced amount ofsoluble protein” is a reduction in soluble protein of greater than about25 percent, preferably about 50 to 95 percent, and more preferably about70 to about 90 percent prior to the concentration step; this reductionis determined taking the protein level at a pH of 4.6 before forewarmingstep as 100 percent and measuring the protein level after theforewarming step. It is generally referred to as “pH 4.6 solubleprotein.” Forewarming can be carried out at temperatures as low as about60° C. although longer times (e.g., greater than several hours) will berequired; preferably temperatures greater than about 70° C. are used toreduce the forewarming period required. For example, effectiveforewarming of the starting dairy liquid can be carried out at atemperature of about 70 to about 100° C. for about 0.5 to about 20minutes, and preferably at about 85 to about 95° C. for about 2 to about6 minutes. In another embodiment, the forewarming is carried out in atwo-stage process comprising a first stage at about 80 to about 100° C.for about 2 to about 6 minutes followed by a second stage at about 100to about 130° C. for about 1 to about 60 seconds. Although not wishingto be limited by theory, it is believed that the serum proteins arepredominately crosslinked to the outer surfaces of the casein proteinmicelles and/or otherwise form aggregates, thereby reducing the solubleprotein. Moreover, such processing allows the production of shelf stableconcentrated milk having 8.5 or more percent protein; indeed, shelfstable concentrated milk products having up to about 13 or 14 percentprotein have been produced using the methods of this invention.

The present invention includes a method of making a stable concentrateddairy liquid, said method comprising: (1) providing a dairy liquidcontaining serum proteins and casein proteins; (2) forewarming the dairyliquid at a temperature of at least about 60° C. for a time sufficient(generally about 30 seconds or more) to form a forewarmed dairy liquidhaving a reduced level of at least about 25 percent of pH 4.6 solubleprotein; (3) concentrating the forewarmed dairy liquid to form a firstintermediate dairy liquid having at least 8.5 percent total protein,wherein the concentration is carried out using ultrafiltration with orwithout diafiltration; (4) adding a stabilizer and a mouthfeel enhancerto the first intermediate dairy liquid to form a second intermediatedairy liquid; and (5) sterilizing the second intermediate dairy liquidat a temperature and for a time sufficient to obtain the stableconcentrated dairy liquid, wherein the stable concentrated dairy liquidhas a F_(o) of at least 5, wherein the second intermediate dairy liquidis resistant to gelation during sterilization, and wherein the stableconcentrated dairy liquid is resistant to gelation for at least aboutsix months of storage under ambient conditions. Preferably the secondintermediate dairy liquid is resistant to gelation and browning duringsterilization and the stable concentrated dairy liquid is resistant togelation and browning for at least about six months of storage underambient conditions. For about 3× milk, preferably the forewarming instep (2) includes a first stage at about 80 to about 100° C. for about 2to about 6 minutes followed by a second stage at about 100 to about 130°C. for about 1 to about 60 seconds; more preferably, the first stage isat about 80 to about 90° C. for about 3 to about 4 minutes and thesecond stage is at about 105 to about 115° C. for about 15 to about 45seconds. For about 5× milk, preferably the forewarming in step (2) is atabout 70 to about 100° C. for about 1.5 to about 6 minutes. These rangesmay, of course, be varied so long as the desired reduction of pH 4.6soluble protein (generally at least about 25 percent reduction,preferably about 50 to about 95 percent reduction, and more preferablyabout 70 to about 90 percent reduction) and the desired stability of thefinal product is achieved. In one embodiment, the sterilization iscarried out by (a) heating the second intermediate dairy liquid to atemperature of about 118 to about 145° C. within about 1 second to about30 minutes and (b) maintaining the heated second intermediate dairyliquid at a temperature of about 118 to about 145° C. for about 1.5seconds to about 15 minutes. If desired, the concentrated dairy liquidcan be homogenized prior to packaging. If desired, the secondintermediate dairy liquid can be standardized prior to the sterilizationstep. Such a standardization step would allow less exacting control overthe ultrafiltration (with or without diafiltration) step sincestandardization of the second intermediate dairy liquid could correctfor variations in the concentration level of the first intermediatedairy liquid from the ultrafiltration step. Using ultrafiltration withor without diafiltration to prepare a 3× to 5× concentrate willgenerally result in a total solids content of about 12 to about 40percent. With such concentration methods, a significant amount of thelactose and minerals are removed during the concentration step. Theconcentrated dairy liquids of this invention contain at least about 8.5percent protein.

The present invention also provides a stable concentrated dairy liquidcomprising about 9 to about 15 percent total protein, about 0.3 to about17 percent fat, about 0.5 to about 5 percent (preferably about 0.5 toabout 1.5 percent) lactose, about 0.05 to about 1 percent stabilizer,and about 0.05 to about 1 percent mouthfeel enhancer; wherein the stableconcentrated dairy liquid has a F_(o) of 5 to about 12 and wherein thestable concentrated dairy liquid is resistant to gelation for at leastabout six months of storage under ambient conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a flowchart illustrating the general method of thepresent invention.

FIG. 2 provides a flowchart illustrating a preferred embodiment of thepresent invention.

FIG. 3 provides a plot illustrating stability and mouthfeel of theconcentrated dairy liquids as provided by the present invention as afunction of the concentrations of stabilizer (i.e., trisodium citrate)and mouthfeel enhancer (i.e., sodium chloride). The methods used toprepare these concentrated dairy liquids are as essentially as describedin Example 1 except that the concentrations of stabilizer and mouthfeelenhancer were varied.

DETAILED DESCRIPTION

The invention is directed to a shelf stable andorganoleptically-pleasing concentrated dairy liquid having greater thanabout 8.5 percent total protein (and preferably greater than about 9percent total protein), wherein the stable concentrated dairy liquid hasreduced level of soluble protein prior to concentration usingultrafiltration with or without diafiltration, wherein a stabilizer anda mouthfeel enhancer are added to the intermediate dairy liquid prior tosterilization, wherein the intermediate dairy liquid is resistant togelation and browning during sterilization, and wherein the stableconcentrated dairy liquid is resistant to gelation and browning for atleast about six months of storage under ambient conditions. Theconcentrated dairy liquid is obtained using thermal processing toachieve the stable concentrated dairy liquid having a sterilizationvalue F_(o) of at least about 5 (preferably at least about 6.5 and morepreferably at least about 7.5). The present invention also includesmethods to obtain such concentrated dairy liquids.

In general, the stable and organoleptically-pleasing dairy liquid isformed through a multi-step thermal process to achieve a desiredsterilization value and product stability characteristics. For instance,the method comprises forewarming, concentrating using ultrafiltrationwith or without diafiltration, and sterilizing steps that provides anoverall thermal treatment that produces the stable concentrated dairyliquid having a F_(o) of at least about 5, preferably at least about6.5, and more preferably at least about 7.5. Importantly, a stabilizerand a mouthfeel enhancer are added to the ultrafiltrated milkconcentrate prior to sterilization.

FIG. 1 illustrates the general method of the present invention. A dairyliquid is homogenized and then forewarmed to a temperature and for atime effective in reducing soluble protein by at least about 25 percent,preferably by about 50 to about 95 percent, and more preferably by about70 to 90 percent (as measured by pH 4.6 soluble protein). The forewarmeddairy liquid is then concentrated to the desired level, generallygreater than about 3× using ultrafiltration type techniques alone orcombined with diafiltration techniques. If ultrafiltration is combinedwith diafiltration, the diafiltration should be carried out during orafter ultrafiltration. After the concentration step, the concentrateddairy liquid is then homogenized. A stabilizer and a mouthfeel enhancerare then added to the homogenized concentrated dairy liquid. After theseadd-backs, the concentrated dairy liquid, which has greater than about8.5 percent total protein, can be packaged and sterilized to a F_(o)greater than 5 to provide the desired stable concentrated dairy liquid.

FIG. 2 illustrates a preferred embodiment of the present invention toproduce concentrated milk. Two-percent milk is homogenized and thenforewarmed (e.g., at about 85° C. for about 5 minutes) to effect atleast about a 25, and preferably at least a 50, percent reduction insoluble protein (measured as pH 4.6 soluble protein). The forewarmedmilk is then concentrated using ultrafiltration, preferably withdiafiltration, to achieve a target composition having about 13 to about14 percent protein, about 8.5 to about 9 percent fat, less than about1.1 percent lactose, and about 24 to about 25 percent solids. Theresulting concentrated composition is then homogenized. Add-backscomprising at least one stabilizer (e.g., about 0.5 to about 1 percenttrisodium citrate), at least one mouthfeel enhancer (e.g., about 0.5 toabout 1 percent sodium chloride), and optional additives (e.g., about0.01 to about 0.3 percent flavor and about 4 to about 8 percent sugar)are then mixed with the homogenized concentrated milk product. Theresulting product is then packaged and sterilized (e.g., retorted) toachieve a F_(o) of at least 5 and to provide the desired stableconcentrated dairy liquid, having a target composition of about 12 toabout 13 percent protein, about 8 to about 8.5 percent fat, less thanabout 1 percent lactose, and about 28 to about 30 percent solids.

For purposes herein, the following terms have the meanings indicated:“Serum protein” refers to the protein content of milk plasma other thancasein (i.e., serum protein refers to whey protein content). “Milkplasma” is the portion of raw milk remaining after removal of the fatcontent. “Casein” generally encompasses casein per se (i.e., acidcasein) or water soluble salts thereof, such as caseinates (e.g.,calcium, sodium, or potassium caseinates, and combinations thereof).Casein amounts and percentages described herein are reported based onthe total amount present of casein and caseinate (excluding the metalcation amount thereof). Casein generally relates to any, or all, of thephosphoproteins in milk, and to mixtures of any of them. An importantcharacteristic of casein is that it forms micelles in naturallyoccurring milk. Many casein components have been identified, including,but not limited to, α-casein (including α_(s1)-casein andα_(s2)-casein), β-casein, γ-casein, κ-casein, and their geneticvariants.

“Reduced fat” milk means about 2 percent fat milk. “Low fat” milk meansabout 1 percent fat milk. “Fat free milk” or “skim milk” both mean lessthan 0.2 percent fat milk. “Whole milk” means not less than about 3.25percent fat milk, and can be standardized or unstandardized. “Milkbutter” means the residual product remaining after milk or cream hasbeen made into butter and contains not less than 3.25 percent fat. “Rawmilk” means milk that has not yet been thermally processed. The milk ormilk products used in the processes of the present invention can bestandardized or non-standardized. The preferred milk is obtained fromcows; other mammalian milk suitable for human consumption can be used ifdesired.

“Shelf-life” means the period of time at which a dairy product can bestored at 70° F. without developing an objectionable organolepticcharacteristic, such as an objectionable aroma, appearance, taste,consistency, or mouthfeel. In addition, an organoleptically acceptabledairy product at a given shelf life will have no off-odor, off-flavor,or brown coloring, will not have a clumped, ropy, or slippery texture,and will remain ungelled. “Stable” or “shelf-stable” means that thedairy product at a given time does not have objectionable organolepticcharacteristics as defined above and is organoleptically acceptable.

“Total milk solids” or “total solids” refers to the total of the fat andsolid-not-fat (SNF) contents. “SNF” refers to the total weight of theprotein, lactose, minerals, acids, enzymes, and vitamins.

Essentially any dairy liquid can be used in the present method.Preferably, the dairy liquid originates from any lactating livestockanimal whose milk is useful as a source of human food. Such livestockanimals include, by way of non-limiting example, cows, buffalos, otherruminates, goats, sheep, and the like. Generally, however, cow's milk ispreferred as the starting material. The milk used may be whole milk,low-fat milk, or skim milk.

Cow's milk contains lactose, fat, protein, minerals, and water, as wellas smaller amounts of acids, enzymes, gases, and vitamins. Although manyfactors may affect the composition of raw cow's milk, it generallycontains about 11 to about 15 percent total solids, about 2 to about 6percent milk fat, about 3 to about 4 percent protein, about 4 to about 5percent lactose, about 0.5 to about 1 percent minerals, and about 85 toabout 89 percent water. Although milk contains many types of proteins,they generally can be grouped into the two general categories: caseinproteins and serum proteins. The minerals, also known as milk salts orash, generally include, as the major components, calcium, sodium,potassium, and magnesium; these cations can combine with phosphates,chlorides, and citrates in milk. Milk fat is mostly comprised oftriglycerides, and smaller amounts of various other lipids. Lactose ormilk sugar (4-O-β-D-galactopyranosyl-D-glucose) is a reducibledisaccharide present in raw milk.

The dairy liquid is initially forewarmed or preheated. Forewarming canbe accomplished using any method or equipment known in the art (e.g.jacketed reactors, heat exchangers, and the like). Not wishing to belimited by theory, it is believed that forewarming initially crosslinksthe serum or whey proteins to the casein micelles present in the milk;most crosslinking is likely to occur to the outer surfaces of themicelles. Such crosslinking will reduce the amount of soluble protein.Again, not wishing to be limited by theory, forewarming may also allowthe whey proteins to interact covalently and/or hydrophobically with themicelles and especially with the outer surfaces of the micelles. Again,not wishing to be limited by theory, it is further believed that theseinteractions accomplish at least two effects. First, the interactionremoves many of the whey proteins from solution; this effect may beimportant because the whey proteins are very reactive at hightemperatures, such as those experienced in sterilization. Secondly, asthe casein micelles become coated with serum or whey proteins,casein-casein interactions should be reduced and/or minimized; thiseffect should reduce the tendency of thermally-induced milk gels toform.

As noted, crosslinking during forewarming decreases the amount ofsoluble protein. The amount of soluble protein can be determined by acidprecipitation followed by liquid chromatography coupled with UV detector(LC-UV). Comparison is made between forewarmed or heat processed samplesand non-heat treated samples to quantify soluble protein fractions. Thereduction in pH 4.6 soluble protein should be at least about 20 percent,preferably about 50 to 95 percent, and more preferably about 70 to about90 percent. More details regarding this method of determining solubleprotein are provided below in the Examples section.

The time and temperature of the forewarming step should be sufficient toobtain the desired reduction of pH 4.6 soluble protein while maintainingthe desired stability of the liquid milk product during sterilizationand subsequent storage. Of course, other parameters, in addition to theforewarming conditions, will effect stability during sterilization andsubsequent storage and balancing of these conditions can be determinedby routine experimentation using the guidance provided herein. Theforewarming or preheating of the dairy liquid is generally carried outat least about 70° C. for at least about 30 seconds to form a preheateddairy liquid having a reduced level of pH 4.6 soluble protein.Preferably, forewarming is conducted at about 70 to about 100° C. forabout 0.5 to about 20 minutes. More preferably, forewarming is conductedat about 85 to about 95° C. for about 2 to about 6 minutes. Otherforewarming conditions may also be used so long as the desired degree ofcrosslinking, generally as measured by a reduction of at least about 20percent of pH 4.6 soluble protein (preferably a reduction of about 50 toabout 95 percent and more preferably about 70 to 90 percent) and thedesired stability of the final product is obtained. Of course, otherforewarming conditions can be used so long as the desired stability isobtained. For example, a two-stage process comprising a first stage atabout 80 to about 100° C. for about 2 to about 6 minutes followed by asecond stage at about 100 to about 130° C. for about 1 to about 60seconds can be used.

After forewarming, the dairy liquid is concentrated to the desiredsolids level. Concentration may be completed by ultrafiltration with orwithout diafiltration. For purposes of this invention, ultrafiltrationis considered to include other membrane concentration methods such asmicrofiltration and nanofiltration. Examples of suitable methodsinvolving microfiltration, ultrafiltration, and diafiltration toconcentrate a dairy liquid are found in U.S. Patent Publication20040067296 (Apr. 8, 2004), which is incorporated herein by reference.It is preferred to concentrate the forewarmed dairy liquid by at leastabout 2.7 fold (and preferably by at least about 3 fold, and morepreferably by at least about 4 fold) to form a concentrated dairy liquidhaving greater than about 8.5 percent protein (and preferably greaterthan about 9 percent). The solid content of the concentrated dairyliquid will depend, at least in part, on the degree of concentrationobtained in the first intermediate dairy liquid. Using ultrafiltration,a significant amount (generally at least about 40 percent and morepreferably at least about 95 percent) of the lactose and minerals areremoved during the concentration step. The concentrated dairy liquids ofthis invention contain at least about 8.5 percent protein. Afterconcentration, the dairy liquid may optionally be chilled to aboutambient temperatures or preferably refrigerated temperatures.

After concentration and optional chilling, effective amounts of astabilizer and a flavor/mouthfeel enhancer are added to the dairyliquid. The stabilizer may be a chaotropic agent, a calcium-bindingbuffer, or other stabilizer which effectively binds calcium to preventgelation or separation of the concentrated dairy liquid during storage.While not wishing to be limited by theory and as is detailed in U.S.Patent Publication 20040067296 (Apr. 8, 2004), it is believed that thecalcium-binding stabilizer prevents gelation or separation of the dairyliquid during any storage prior to the subsequent sterilization. Anybuffer or chaotropic agent or stabilizer which binds calcium may beused. Examples of calcium-binding buffers, stabilizers, and chaotropicagents include citrate and phosphate buffers, such as disodiumphosphate, dipotassium phosphate, disodium citrate, trisodium citrate,EDTA, and the like as well as mixtures thereof. Examples of chaotropicagents include dodecyl sodium sulfate (SDS) and urea. A preferredcalcium-binding buffer or stabilizer is a citrate buffer, such astrisodium citrate. Suitable mouthfeel enhancers include sodium chloride,potassium chloride, sodium sulfate, and mixtures thereof. Preferredmouthfeel enhancers include sodium chloride and potassium chloride aswell as mixtures thereof; sodium chloride is the most preferredmouthfeel enhancer. Flavors and other additives such as sugar,sweeteners (natural and/or artificial), emulsifiers, fat mimetics,maltodextrin, fibers, starches, gums, and enzyme-treated, cultured,natural, and artificial flavors or flavor extracts can be added so longas they do not significantly and adversely effect either the stabilityor mouthfeel characteristics. Lactose can also be added if desired;increased lactose may, however, increase the potential of theconcentrated milk product to brown either during sterilization orstorage and thus should typically be used only where such browning doesnot present a significant problem (e.g., for use in dark coloredbeverages and the like). If additional lactose is not added, the lactoselevels of the stable concentrated milk product are generally less thanabout 1 percent. Lactose can, if desired, be added up to about 5 percent(but preferably up to only about 1.5 percent); browning, as noted, mayincrease with increasing lactose levels. Preferably, such flavors,especially sugars and/or sweeteners, are added to the concentrated milkproducts of this invention. The effective amount of the stabilizer andmouthfeel enhancer depends on the specific dairy liquid used as thestarting material, the concentration desired, and the calcium bindingcapacity of the specific stabilizer used. However, in general, about 0.1to about 1 percent of trisodium citrate, about 0.1 to about 1 percentsodium chloride, about 1 to 10 percent sugar, and about 0.01 to 0.3percent other flavors are effective in the present invention when cow'smilk is the starting dairy liquid.

FIG. 3 provides an illustrative plot of stability and sensory aspects asa function of the concentrations of stabilizer (i.e., trisodium citrate)and mouthfeel enhancer (i.e., sodium chloride). The space within theoval represents the best combination of stability and sensoryproperties; these samples remain fluid during processing and uponstorage and have good to excellent mouthfeel. Based on this chart,preferred ranges for both trisodium citrate and sodium chloride areabout 0.1 to about 1 percent within the limits of the data generated. Ofcourse, as one skilled in the art would realize, the oval could extendinto the upper right hand side of the chart if further data wasgenerated; at some point, however, the product may become too salty tobe satisfactory (generally expected at sodium chloride levels of greaterthan about 1.1 to about 1.2 percent). As one skilled in the art wouldalso realize, the “best combination” space may move or vary depending onthe specific combination of stabilizer(s) and/or mouthfeel enhancer(s)used, as well as depending on other variables associated with theprocess (e.g., forewarming conditions, ultrafiltration conditions,sterilization conditions, and the like). For a particular set ofcomponents and processing conditions, one of ordinary skill couldproduce a similar graph to guide control and optimization of the processand product.

After concentration and optional chilling, the dairy liquid is thenmixed with the stabilizer and flavor/mouthfeel enhancer (and optionalflavors or other additives if desired) and sterilized to form thestable, sterile, concentrated dairy liquid. Preferably, sterilization iscarried out using retorting conditions. Optionally, if the concentrateddairy liquid needs to be diluted to meet a targeted concentration, thedilution should be accomplished prior to sterilization. Preferably, thedairy liquid is packaged, sealed, and then subjected to sterilizationtemperatures in any suitable equipment. Sterilization is carried outunder time and temperature conditions to achieve a F_(o) of at least 5.Generally, the sterilization process consists of a come-up or heatingtime, a holding time, and a cool-down time. During the come-up time, atemperature of about 118 to about 145° C. is achieved in about 1 secondto about 30 minutes. The temperature is then maintained at about 118 toabout 145° C. for about 1.5 seconds to about 15 minutes. The temperatureis then cooled below about 25° C. within about 10 minutes or less.Preferably the sample is gently agitated (e.g., rotating the container)during sterilization to minimize “skin” formation.

The overall thermal treatment (i.e., forewarming, concentration, andsterilization) is controlled to produce a stable concentrated dairyliquid having a total protein content greater than about 8.5 percent andpreferably greater than about 9 percent while providing a F_(o) of atleast about 5 and a shelf life of at least about six months underambient conditions. Generally, the stable concentrated dairy liquid ofthe present invention has a viscosity of about 70 to about 4000 mPa andpreferably about 100 to about 300 mPa at ambient temperatures. As noted,the overall thermal treatment achieves a sterilization value F_(o) of atleast 5, and achieves product characteristics that render theconcentrated dairy liquid resistant to gelation and browning during thehigh temperature processing and also for greater than six months ofambient storage.

As noted, the concentration step is carried out using ultrafiltration,preferably with diafiltration, using a membrane pore size large enoughto permit a portion of the lactose and minerals to pass through thepores with water as the permeate, while the retentate includesessentially all the protein and fat content.

For example, milk can be subjected to a membrane separation treatment toseparate a protein-enriched “retentate” from a lactose-enrichedpermeate. The type of milk processed according to this invention is notparticularly limited, and includes, for example, whole milk, skim milk,reduced fat milk, low fat milk, butter milk, and combinations thereof.

In one embodiment, membrane filtration procedure parameters used includea molecular weight (MW) cut off of approximately 10,000 using a porouspolysulfone membrane, about 35 to about 65 psig applied pressure, and aprocessing temperature of about 110 to about 140° F. (about 43 to about60° C.). In one embodiment, lactose and minerals pass the membrane in anabout 50 percent separation ratio, and the retentate comprises about 100percent of the fat and protein introduced by combined feed stream, about50 percent of lactose, and about 50 percent of free minerals relative tothe feed stream. Diafiltration serves to keep the lactose concentrationin the retentate below 4 percent.

As noted above, the concentrated dairy liquid can be homogenized priorto packaging. In general, homogenization may be carried out at any timeafter the desired dairy composition is prepared and before packaging tohelp break up and disperse milk fat content, if any, throughout thedairy product to better ensure a smooth, uniform texture.Homogenization, if used, may be performed in one or multiple stages. Forinstance, in one non-limiting embodiment a first homogenization stagecan be performed at about 1,500 psi and a second stage at about 500 psiin an industry standard homogenizer. The homogenate may be cooled if itwill not be immediately conducted to a packaging operation. For example,the homogenate may be cooled as it flows through a regeneration andcooling section of a plate heat exchanger of a standard homogenizer.Other homogenization schemes applicable to milk products also may beused.

The packaging technique used is not particularly limited as long as itpreserves the integrity of the dairy product sufficient for theapplicable shelf life of the dairy product. For example, milkconcentrates can be sterilized or retorted in glass bottles or gable-topcartons, and so forth, which are filled, sealed, and the contents arethen thermally processed. The dairy products also can be packaged inlarger quantities such as in conventional bag-in-box containers ortotes. In one embodiment, presterilized bottles or foil-lined gable-topcarton materials may be used. Food packaging systems designated asextended shelf life (ESL) or aseptic packaging systems may also be used,but the invention is not limited thereto. The useful food packagingsystems include conventional systems applied or applicable to flowablefood products, especially milk products and fruit juices. As notedabove, preferably the samples are gently agitated (e.g., rotating thecontainer) during sterilization to minimize “skin” formation. The dairyproduct also may be loaded into and transported in bulk form via tankertrucks or rail car tankers.

Although not required to achieve the extended shelf lives associatedwith dairy products of the present invention, pasteurization and/orultra-high temperature (UHT) procedures also may be applied to dairyproducts of the present invention in the event of process interruptionand/or for further shelf life enhancement. UHT products areultrapasteurized and then packaged in sterilized containers. Moreover,one advantage of the present invention is that UHT processing is notrequired to obtain extended shelf lives. For example, if theultrafiltered/diafiltered product is to be held for an extended periodof time (e.g., greater than about a day) before continuing the process,pasteurization of the ultrafiltered product may be undertaken. Ifdesired, intermediate products in the process may be pasteurized ifdesired so long as the pasteurization does adversely effect stability ormouthfeel of the final product.

The stable concentrated dairy liquid, in a preferred form, is anorganoleptically pleasing milk that may be sealed in cartridges or podsto be used in any number of beverage preparation machines. Examples ofpreferred uses and beverage preparation machines can be found in U.S.patent application Ser. No. 10/763,680, filed Jan. 23, 2004, now U.S.Pat. No. 7,640,843 issued on Jan. 5, 2010, and owned by the sameassignee as the present specification. This just-identified patentapplication is incorporated herein by reference. The concentration ofthe milk is beneficial because it allows for larger volumes of the milkto be dispensed from the beverage preparation machines while being ableto store a smaller package with less quantity of liquid.

For instance, a cartridge of the concentrated milk may be used toproduce an authentic looking frothy milk-based foam desired by consumersin a cappuccino-style beverage. The cartridge of the stable concentratedmilk is also suitable for foaming using a low pressure preparationmachine and cartridge as described in U.S. patent application Ser. No.10/763,680 using only pressures below about 2 bar.

In addition, a milk beverage may also be formed using the stableconcentrated milk. For example, a beverage may be formed by mixing thestable concentrated milk with an aqueous medium. The milk beverage mayalso be dispensed from a cartridge containing the stable concentratedmilk, also described in U.S. patent application Ser. No. 10/763,680, bypassing an aqueous medium through the cartridge to form a beverage bydilution. The concentrated milk may preferably be mixed or diluted withthe aqueous medium in a ratio of between about 1:1 to about 6:1.

The following examples are intended to illustrate the invention and notto limit it. Unless otherwise indicated, all percentages are by weight.All references, including provisional applications, patent publications,patents, and other references or publications, cited in the presentspecification are hereby incorporated by reference.

EXAMPLES

Analytical Method for pH 4.6 Soluble Protein: The analysis of pH 4.6soluble proteins is specific for the quantization of a-lactalbumin and13-lactoglobulin serum proteins. A summary of the sample preparation andanalysis is described below. The method is based on methodologiespublished in J. Agric. Food Chem. 1996, 44, 3955-3959 and Int. J. FoodSci. Tech. 2000, 35, 193-200 with modifications to make it amendable toHPLC-mass spectrometry.

The sample preparation starts with weighing out 50.00±0.02 g of materialin a 100 mL beaker. A stir bar was placed in the beaker and stirredvigorously for 5 minutes to obtain a stable pH reading. Next, the pH waslowered to 4.6 (22±2° C.) by the drop wise addition of HC1. Once the pHreading was stable for ca. 5 minutes, a portion was poured into adisposable polypropylene vial and centrifuged (15 minutes at 4° C. and2600×g). A portion of the supernatant below the fat layer, but above theprotein pellet, was removed with a disposable pipette.

Appropriate dilutions were made with 0.1 M (pH 6.7) phosphate buffer(Sigma, St. Louis, Mo., USA) to fit the calibration range of standards.Portions of the diluted samples were placed in micro-spin filter tubescomposed of a 0.45 μm regenerated cellulose membrane and centrifuged (1minute at room temperature and 2000×g).

Samples were analyzed by reversed-phase HPLC using two PLRP-S 5 mm,300A, 150×2.1 mm columns in series (Polymer Laboratories Inc., Amherst,Mass.). The mobile phase was a linear binary gradient from 64:36 to47:53 water:acetonitrile both containing 5% formic acid in 15 minutes.The flow-rate was 225 μL/min with an injection volume of 15 μL. The UVabsorption at 280 nm was recorded for quantitation. All isoforms ofαα-lactalbumin and β-lactoglobulin, which were chromatographicallyresolved, were summed together as a group, respectively.

Analytical Method for Total Protein: The total protein after theconcentrating step was measured by using the AOAC Official Method 991.20Nitrogen (Total) in Milk.

Example 1

This Example illustrates the preparation of 4.5× milk using the processof this invention. Three concentrated milk products were preparedaccording to the formulas described in Table 1. Inventive Samples 1 and2 represent examples of the present invention and are compared to acomparison sample.

All inventive products and the comparison product were prepared usingthe same batch of concentrated 2% milk. The reduced fat milk wasforewarmed by heating to 88° C. for about 5 minutes (pH soluble proteinreduced by greater than about 50 percent) and then concentrated toprovide a 4.5× concentrate product using ultrafiltration withdiafiltration. The membrane filtration was conducted at 120° F. and40-60 psig. The membrane filtration system used was a polysulfonemembrane pore sized to provide about a 10,000 MW cutoff. The fresh 2%milk was produced with 200 lbs being concentrated to 4.5× in 5 hourswith about 80 pounds diafiltration water added during this time.

After ultrafiltration with diafiltration, the concentrated milk washomogenized at 1,500 psi and cooled at 45° F., mixed with variousamounts of salts and sugar and stored until packaged and retorted.Stabilizers and mouthfeel enhancers were added to Inventive Samples 1and 2 as indicated in Table 1 before packaging and retorting. Thecomparison milk product represented a milk concentrate without addedstabilizer or mouthfeel enhancer. All samples were packaged in 350 mLglass bottles or gable-top cartons, and retorted under the temperatureand time conditions indicated in Table 1. All three samples had morethan about 10 percent protein.

TABLE 1 Comparative Inventive Inventive Formula Sample Sample 1 Sample 24.5X UF/DF 2% milk 100 93.1 90.5 concentrate Flavor (%) 0 0.02 0.02Trisodium Citrate (%) 0 0.3 0.7 Salt (%) 0 0.6 0.4 Sucrose (%) 0 6.0 8.5Total (%) 100 100 100 Retort Conditions 8 min/ 8 min/253° F./ 8 min/253°F./GB (time/temp/package*) 253° F./GB GB Product Quality** 1 2 2 (0Time) Product Quality** 1 2 2 (3 months at 70° F.) *“GB” - glass bottlewas used as the packaging container; “GC” - gable-top carton was used.**Mouthfeel measurements were at 60° C. using samples diluted back to 1Xmilk. Organoleptic product quality score: 1 = watery, thin mouthfeel,bland taste; 2 = milky, 2% milk-like consistency and color, and pleasantdairy flavor.

The 4.5× UF/DF 2% milk composition including 24.5% total solids, 13.6%protein, 8.8% fat, 0.9% lactose, and 1.2% ash. Stabilizers and mouthfeelenhancers (i.e., 0.33% trisodium citrate, 0.55% sodium chloride, 6%sucrose, and 0.02% flavor concentrate for Inventive Sample 1; 0.66%trisodium citrate, 0.275% sodium chloride, 8.5% sucrose, and 0.02%flavor concentrate for Inventive Sample 2) were added prior to retortingunder the conditions presented in Table 1.

Organoleptic evaluations of the various dairy products were performed onfreshly packaged, retorted products and after storage at 70° F. for onemonth or three months. Inventive Samples 1 and 2 were white, flowablewith about an olive-oil consistency, and exhibited no signs of browningor gelling immediately after being prepared or after storage for up toeight months. The reconstituted dairy products from Inventive Samples 1and 2 (diluted to 1× concentration and evaluated after 3 months storage)had a very good dairy flavor and pleasant mouthfeel similar to that of2% milk. In contrast, the Comparative Sample had watery-like mouthfeeland bland taste with little dairy flavor.

Similar results were obtained using other types of milk (i.e., skimmilk, reduced fat milk, and whole milk, as well as combinationsthereof). Similar concentrated milk samples prepared by the methoddescribed herein have been found to be stable (i.e., no gelation) for upto about 8 months (i.e., as of the filing date of this specification) atambient temperatures; stability testing is ongoing as of the filing dateof this specification.

Example 2

Experiments similar to Example 1 were carried out using different levelsof the stabilizers and mouthfeel enhancers. All inventive products andthe comparison product were prepared using the same batch ofconcentrated 2% milk and the same techniques as described in Example 1(i.e., reduced fat milk was forewarmed by heating to 88° C. for about 5minutes and then concentrated to provide a 4.5× concentrate productusing ultrafiltration/diafiltration). The pH 4.6 soluble protein wasreduced by about 70 percent during the forewarming step.

Stabilizers and mouthfeel enhancers were added to Inventive Samples 2 to7 in Table 2 before packaging and retorting. The comparison milk product1 represented a milk concentrate without added stabilizer or mouthfeelenhancer. All samples were packaged in 350 mL glass bottles and retortedunder the temperature and time conditions as described in Example 1. Allsamples had more than about 10 percent protein.

Organoleptic evaluations of the various dairy products were performed onfreshly packaged, retorted products and after storage at 70° F. for 1week. Evaluations were conducted by a panel of seven trained foodtechnologists. Mouthfeel ratings fell into three categories: low (i.e.,unacceptable), medium (i.e., good), and high (i.e., excellent); the lowranking was comparable to a ranking of 1 in Examples 1 and 2, whereasmedium and high are comparable to a ranking of 2. High rating indicatesthat the milk had a full mouthfeel similar to that of 2% milk. Incontrast, low rating indicates that milk had watery-like mouthfeel.Inventive Samples 2 to 7 remained fluid without browning or gellingimmediately after being prepared or after storage for at least 1 month.

TABLE 2 Comparative Inventive Samples Formula Sample 1 2 3 4 5 6 7 4.5XUF/DF 100 91.5 91.9 93.7 92.7 91.5 93.2 2% milk concentrate Flavor (%) 00.02 0.02 0.02 0.02 0.02 0.02 Trisodium 0 0.9 0.8 0.1 0.5 1.5 0.5citrate (%) NaCl (%) 0 1.5 1.3 0.2 0.8 1.0 0.3 Sucrose (%) 0 6 6 6 6 6 6Total (%) 100 100 100 100 100 100 100 Product Low High High Medium HighHigh Medium Quality* (1 week) *Mouthfeel measurements were at 60° C.using samples diluted back to 1X milk. Organoleptic product qualityscore: Low = watery, thin mouthfeel, bland taste; Medium = increasedmouthfeel and dairy notes but less mouthfeel than 2% milk; High = milky,2% milk-like consistency, color, and mouthfeel with pleasant dairyflavor.

Example 3

Additional experiments similar to Example 2 were also carried out usingdifferent stabilizer and/or mouthfeel enhancers. All inventive productsand the comparison product were prepared using the same batch ofconcentrated 2% milk and the same techniques as described in Example 1(i.e., reduced fat milk was forewarmed by heating to 88° C. for about 5minutes and then concentrated to provide a 4.5× concentrate productusing ultrafiltration/diafiltration). The pH 4.6 soluble protein wasreduced by about 70 percent during the forewarming step.

Stabilizers and mouthfeel enhancers were added to Inventive Samples 2 to7 in Table 3 before packaging and retorting. The comparison milk product1 represented a milk concentrate without added stabilizer or mouthfeelenhancer. All samples were packaged in 350 mL glass bottles and retortedunder the temperature and time conditions as described in Example 1. Allsamples had more than about 10 percent protein.

Organoleptic evaluations of the various dairy products were performed onfreshly packaged, retorted products and after storage at 70° F. for 1week. Evaluations were conducted by the same panel using the sameranking categories as in Example 2. Inventive Samples 2 to 7 remainedfluid without browning or gelling immediately after being prepared orafter storage for at least 1 month.

TABLE 3 Comparative Inventive Samples Formula Sample 1 2 3 4 5 6 7 4.5XUF/DF 100 93.0 93.0 93.1 93.1 93.1 93.0 2% milk concentrate Flavor (%) 00.02 0.02 0.02 0.02 0.02 0.02 Trisodium 0 0.3 0.3 0 0 0 0.3 citrate (%)Tripotassium 0 0 0 0.4 0 0 0 citrate (%) Disodium 0 0 0 0 0.3 0 0phosphate (%) Sodium 0 0 0 0 0 0.3 0 Hexameta- phosphate (%) NaCl (%) 00 0.3 0.6 0.6 0.6 0 KCl (%) 0 0.7 0.4 0 0 0 0 Na₂SO₄ (%) 0 0 0 0 0 0 0.7Sucrose (%) 0 6 6 6 6 6 6 Total (%) 100 100 100 100 100 100 100 ProductLow High High High High High Medium Quality* (1 week) *Mouthfeelmeasurements were at 60° C. using samples diluted back to 1X milk.Organoleptic product quality score: Low = watery, thin mouthfeel, blandtaste; Medium = increased mouthfeel and dairy notes but less mouthfeelthan 2% milk; High = milky, 2% milk-like consistency, color, andmouthfeel with pleasant dairy flavor.

The stabilizers (i.e., trisodium citrate, tripotassium citrate, disodiumphosphate, and sodium hexametaphosphate) produced superior milkconcentrates when used in combination with NaCl and/or KC1 as themouthfeel enhancer. Sodium sulfate, when used as the mouthfeel enhancer,produced an acceptable, but not superior, concentrated milk product.

Example 4

This Example compares the use of ultrafiltration with and withoutdiafiltration. The reduced fat (2%) milk was forewarmed by heating to88° C. for about 5 minutes and then concentrated to provide a 4.5×concentrate product using ultrafiltration only, or with 1× equal volumediafiltration (abbreviated as 1× DF) or 1× equal volume diafiltrationfollowed by another 1× equal volume diafiltration (abbreviated as 2×DF). Diafiltration, when used, was carried out after ultrafiltration.Otherwise, the methods used were as described in Example 1. The pH 4.6acid soluble protein was reduced by 78% using the forewarming step.Table 4 lists sample formulation and sensory evaluation.

Comparative Samples 1-3 were concentrated milk without any add backs.Inventive Samples 4-6 contained the stabilizing salt and mouthfeelenhancer, which were added before packaging and retorting. All sampleswere packaged in 350 mL glass bottles and retorted under the temperatureand time conditions as described in Example 1. All samples had more thanabout 10 percent protein.

Organoleptic evaluations of the various dairy products were performed onfreshly packaged, retorted products and after storage at 70° F. within 1week using the same methods as described in Example 1.

TABLE 4 Comparative Samples Inventive Samples Formula 1 2 3 4 5 6 4.5XUF, no DF 100 0 0 93.1 0 0 4.5X UF, 1X DF 0 100 0 0 93.1 0 4.5X UF, 2XDF 0 0 100 0 0 93.1 Flavor (%) 0 0 0 0.02 0.02 0.02 Trisodium citrate(%) 0 0 0 0.3 0.3 0.3 NaCl (%) 0 0 0 0.6 0.6 0.6 Sucrose (%) 0 0 0 6 6 6Total (%) 100 100 100 100 100 100 Product Quality* Low Low Low High HighHigh (1 week) *Mouthfeel measurements were at 60° C. using samplesdiluted back to 1X milk. Organoleptic product quality score: Low =watery, thin mouthfeel, bland taste; Medium = increased mouthfeel anddairy notes but less mouthfeel than 2% milk; High = milky, 2% milk-likeconsistency, color, and mouthfeel with pleasant dairy flavor.

Inventive Samples 4 to 6 were fluid without browning or gellingimmediately after being prepared or after storage for at least 1 monthand had excellent mouthfeel. Comparative Examples 1 to 3, although theydid not gel, had unacceptable mouthfeel properties.

Example 5

This Example compares the addition of the stabilizer and mouthfeelenhancer alone or in combination. The procedures used were as describedin Example 1 (i.e., forewarming at 88° C. for about 5 minutes and thenconcentrated to 4.5× using ultrafiltration and diafiltration). The pH4.6 soluble protein was reduced by 74 percent after the forewarmingstep. Table 5 lists sample formulation and sensory evaluation. Allsamples were packaged in 350 mL glass bottles and retorted under thetemperature and time conditions as described in Example 1. All sampleshad more than about 10 percent protein.

Organoleptic evaluations were carried out on freshly packaged, retortedproducts and after storage at 70° F. for one week using the sameprocedures as in Example 1. Inventive Samples 4-7 were fluid withoutbrowning or gelling immediately after being prepared or after storagefor at least 1 month.

TABLE 5 Comparative Samples Inventive Formula 1 2 3 Sample 4.5X UF, 2XDF 100 93.7 93.4 93.1 Flavor (%) 0 0.02 0.02 0.02 Trisodium citrate 00.33 0 0.33 (%) NaCl (%) 0 0 0.6 0.55 Sucrose (%) 0 6 6 6 Total (%) 100100 100 100 Product Quality* Low Gelled Gelled High (1 week) *Mouthfeelmeasurements were at 60° C. using samples diluted back to 1X milk.Organoleptic product quality score: Low = watery, thin mouthfeel, blandtaste; Medium = increased mouthfeel and dairy notes but less mouthfeelthan 2% milk; High = milky, 2% milk-like consistency, color, andmouthfeel with pleasant dairy flavor. Gelled samples were not evaluatedfor mouthfeel or other organoleptic properties.

Separate addition of only the stabilizer (such as trisodium citrate) atlow levels (<about 0.2 percent) or the mouthfeel enhancer (such as NaCl)at low levels (<about 0.275 percent) provided milk stability but a lessthan desirable level of mouthfeel. Addition of only the stabilizer athigh levels (>about 0.2 percent) or the mouthfeel enhancer at (>about0.275 percent) resulted in gelation during retorting. When both thestabilizer and mouthfeel enhancer were used, excellent milk stabilityand good to excellent mouthfeel were obtained.

Example 6

This Example demonstrates that monovalent cations, such as potassium andsodium, contribute to milk stability and mouthfeel whereas divalentcations provide unacceptable results (i.e., milk gelation). Theprocedures used were as described in Example 1. The followingformulations were prepared and evaluated.

TABLE 6 Comparative Samples Inventive Formula 1 2 3 4 5 Sample 4.5X UF,100 93.9 93.8 93.7 93.1 93.1 2X DF Flavor (%) 0 0.02 0.02 0.02 0.02 0.02Trisodium 0 0.33 0.33 0.33 0.33 0.33 citrate (%) NaCl (%) 0 0 0 0 0 0.55MgCl₂•6H₂O 0 0.96 0.64 0 0 0 (%) CaCl₂ (%) 0 0 0 0.52 0.35 0 Sucrose (%)0 6 6 6 6 6 Total (%) 100 100 100 100 100 100 Product Low Gelled GelledGelled Gelled High Quality* (1 week) *Mouthfeel measurements were at 60°C. using samples diluted back to 1X milk Organoleptic product qualityscore: Low = watery, thin mouthfeel, bland taste; Medium = increasedmouthfeel and dairy notes but less mouthfeel than 2% milk; High = milky,2% milk-like consistency, color, and mouthfeel with pleasant dairyflavor. Gelled samples were not evaluated for mouthfeel or otherorganoleptic properties.

The attempted use of divalent cation salts resulted in gelation afterretorting. Only the Inventive Sample (containing trisodium citrate andsodium chloride) provided an acceptable product.

While the invention has been particularly described with specificreference to particular process and product embodiments, it will beappreciated that various alterations, modifications and adaptations maybe based on the present disclosure, and are intended to be within thespirit and scope of the present invention as defined by the followingclaims. For instance, while the present invention has been exemplifiedwith respect to bovine milk and milk products, it will be appreciatedthat the invention is generally applicable to any mammalian milk or milkproduct derived from mammalian milk.

1-23. (canceled)
 24. A stable concentrated dairy liquid comprising about9 to about 15 percent total protein, about 0.3 to about 17 percent fat,about 0.5 to about 5 percent lactose, about 0.05 to about 1 percentstabilizer, and about 0.05 to about 1 percent mouthfeel enhancer;wherein the stable concentrated dairy liquid has a F_(o) of 5 to about12 and wherein the stable concentrated dairy liquid is resistant togelation for at least about six months of storage under ambientconditions.
 25. The stable concentrated dairy liquid of claim 24,wherein the lactose is about 0.5 to about 1.5 percent.
 26. The stableconcentrated dairy liquid of claim 24, wherein the stable concentrateddairy liquid is obtained by a process comprising (1) providing a dairyliquid containing serum proteins and casein proteins; (2) forewarmingthe dairy liquid at a temperature of at least about 60° C. for a timesufficient to form a forewarmed dairy liquid having a reduced level ofat least about 25 percent of pH 4.6 soluble protein; (3) concentratingthe forewarmed dairy liquid to form a first intermediate dairy liquidhaving at least 9 percent total protein, wherein the concentration iscarried out using ultrafiltration with or without diafiltration; (4)adding the stabilizer and the mouthfeel enhancer to the firstintermediate dairy liquid to form a second intermediate dairy liquid;and (5) sterilizing the second intermediate dairy liquid at atemperature and for a time sufficient to obtain the stable concentrateddairy liquid with F_(o) of at least 5, wherein the second intermediatedairy liquid is resistant to gelation during sterilization.
 27. Thestable concentrated dairy liquid of claim 26, wherein the forewarmingcomprises a first stage at about 80 to about 100° C. for about 2 toabout 6 minutes followed by a second stage at about 100 to about 130° C.for about 1 to about 60 seconds and wherein the reduced level of pH 4.6soluble protein in the forewarmed dairy liquid is about 50 to about 95percent.
 28. The stable concentrated dairy liquid of claim 26, whereinthe forewarming comprises heating to about 70 to about 100° C. for about1.5 to about 6 minutes and wherein the reduced level of pH 4.6 solubleprotein in the forewarmed dairy liquid is about 50 to about 95 percent.29. The stable concentrated dairy liquid of claim 26, wherein thestabilizer is added to the first intermediate dairy liquid at about 0.1to about 1 percent, and the stabilizer is selected from the groupconsisting of disodium phosphate, dipotassium phosphate, disodiumcitrate, trisodium citrate, and mixtures thereof; and wherein themouthfeel enhancer is added to the first intermediate dairy liquid atabout 0.1 to about 1 percent and the mouthfeel enhancer is selected fromthe group consisting of sodium chloride, potassium chloride, sodiumsulfate, and mixtures thereof.
 30. The stable concentrated dairy liquidof claim 26, wherein the stabilizer is added to the first intermediatedairy liquid at about 0.1 to about 1 percent, and the stabilizer isselected from the group consisting of disodium phosphate, dipotassiumphosphate, disodium citrate, trisodium citrate, and mixtures thereof;and wherein the mouthfeel enhancer is added to the first intermediatedairy liquid at about 0.1 to about 1 percent and the mouthfeel enhanceris selected from the group consisting of sodium chloride, potassiumchloride, sodium sulfate, and mixtures thereof.
 31. The stableconcentrated dairy liquid of claim 28, wherein the stabilizer is addedto the first intermediate dairy liquid at about 0.1 to about 1 percent,and the stabilizer is selected from the group consisting of disodiumphosphate, dipotassium phosphate, disodium citrate, trisodium citrate,and mixtures thereof; and wherein the mouthfeel enhancer is added to thefirst intermediate dairy liquid at about 0.1 to about 1 percent and themouthfeel enhancer is selected from the group consisting of sodiumchloride, potassium chloride, sodium sulfate, and mixtures thereof. 32.The stable concentrated dairy liquid of claim 29, wherein the stabilizeris disodium phosphate or trisodium citrate and the mouthfeel enhancer issodium chloride.
 33. The stable concentrated dairy liquid of claim 30,wherein the stabilizer is disodium phosphate or trisodium citrate andthe mouthfeel enhancer is sodium chloride.
 34. The stable concentrateddairy liquid of claim 31, wherein the stabilizer is disodium phosphateor trisodium citrate and the mouthfeel enhancer is sodium chloride. 35.The stable concentrated dairy liquid of claim 24 wherein the stableconcentrated dairy liquid is packaged in a sealed container suitable foruse in a beverage making machine.
 36. The stable concentrated dairyliquid of claim 26, wherein the stable concentrated dairy liquid ispackaged in a sealed container suitable for use in a beverage makingmachine.
 37. The stable concentrated dairy liquid of claim 29, whereinthe stable concentrated dairy liquid is packaged in a sealed containersuitable for use in a beverage making machine.
 38. The stableconcentrated dairy liquid of claim 30, wherein the stable concentrateddairy liquid is packaged in a sealed container suitable for use in abeverage making machine.
 39. The stable concentrated dairy liquid ofclaim 31, wherein the stable concentrated dairy liquid is packaged in asealed container suitable for use in a beverage making machine.
 40. Thestable concentrated dairy liquid of claim 24, wherein the stableconcentrated dairy liquid is standardized to a predeterminedconcentration level of about 3× to about 5×.
 41. The stable concentrateddairy liquid of claim 26, wherein the second intermediate dairy liquidis standardized prior to sterilization such that the stable concentrateddairy liquid has a predetermined concentration level of about 3× toabout 5×.
 42. The stable concentrated dairy liquid of claim 29, whereinthe second intermediate dairy liquid is standardized prior tosterilization such that the stable concentrated dairy liquid has apredetermined concentration level of about 3× to about 5×.
 43. Thestable concentrated dairy liquid of claim 30, wherein the secondintermediate dairy liquid is standardized prior to sterilization suchthat the stable concentrated dairy liquid has a predeterminedconcentration level of about 3× to about 5×.
 44. The stable concentrateddairy liquid of claim 31, wherein the second intermediate dairy liquidis standardized prior to sterilization such that the stable concentrateddairy liquid has a predetermined concentration level of about 3× toabout 5×.
 45. The stable concentrated dairy liquid of claim 24, whereinthe stable concentrated dairy liquid contains about 0.1 to about 1percent of trisodium citrate, about 0.1 to about 1 percent sodiumchloride, about 1 to 10 percent sugar, and about 0.01 to 0.3 percentflavors and wherein the stable concentrated dairy liquid is resistant tobrowning for at least about six months of storage under ambientconditions.
 46. The stable concentrated dairy liquid of claim 26,wherein the stable concentrated dairy liquid contains about 0.1 to about1 percent of trisodium citrate, about 0.1 to about 1 percent sodiumchloride, about 1 to 10 percent sugar, and about 0.01 to 0.3 percentflavors and wherein the stable concentrated dairy liquid is resistant tobrowning for at least about six months of storage under ambientconditions.